1. Field of Invention
The present invention relates to a driving circuit. More particularly, the present invention relates to a light emitting diode driving circuit.
2. Description of Related Art
Recently, electronic devices with integrated display panels have become popular. For example, mobile phones, the PDA and the MP3 player all have a display panel. The display panel needs a light source, such as a backlight module, to enable the display of figures and words. The backlight module usually includes a lot of light emitting diodes that are driven by the light emitting diode driving circuit.
FIG. 1 shows the conventional light emitting diode back light module. The light emitting diode back light module includes constant voltage Vin, the resistor R1, the resistor R2, the light emitting diodes LED1, and the light emitting diodes LED2. The resistor R1 and resistor R2 are electrically connected to the light emitting diodes LED1 and LED2 respectively for limiting the current volume flowing through the light emitting diodes LED1 and LED2. The constant voltage Vin is electrically connected to the resistor R1 and resistor R2 for providing the light emitting diode LED1 and LED2 the potential.
In order to turn on the light emitting diodes LED1 (or LED2) connected serially, the constant voltage Vin needs to provide a potential greater than the sum of light emitting diodes light threshold voltages, and the luminance of the light emitting diode LED1 is corresponding to the current volume flowing through the light emitting diode LED1.
Therefore, there is a need for a new light emitting diode driving circuit which can improve the performance of the light emitting diode and the driving circuit.